You're a prudent parent, and you protect your children from behavior that is needlessly risky or harmful. You don't let them ride a bicycle without first putting on a helmet. You wait with them for the school bus, or drive them to school yourself. You wouldn't dream of letting them drink alcohol, and if you caught them with cigarettes, you'd go through the roof.

So why do you let them watch so much TV?

For turning brains into mush, you can't do better than television. The "vast wasteland" Newton Minow deplored in 1961 is infinitely vaster now -- a largely unrelieved wilderness of mindless, stupefying entertainment, where dysfunction vies for predominance with vulgarity, and where the insatiable hunger for ratings eventually overpowers every consideration of taste, morality, and intellect.

TV isn't called the idiot box for nothing. Even at its best it replaces engaged and active thought with passive and sedentary spectating, while at its worst it destroys children's innocence, inuring them to violence, mockery, and crude sexualization. Television is by definition a visual medium; it appeals not to the brain but to the eye. You don't have to study hypnosis to understand how easily the eye can be exploited to undermine alertness, focus, and good judgment. Just look at the dazed and vacant expression on the face of a youngster watching TV. Most parents would be calling 911 if their child drank something that caused such a reaction. Why doesn't the zoned-out oblivion induced by TV cause parents to panic? Is it because they're hooked on it too?

"Television Addiction Is No Mere Metaphor," reported Scientific American a few years back, and the identity of the world's foremost TV junkies is no mystery. It's us. According to the Organisation for Economic Co-operation and Development, American households in 2007 watched an average of 8.2 hours of television per day, roughly twice as much as viewers anywhere else. And we are awash in television outside the home as well: in gyms, bars, and airport terminals, of course, but increasingly even in public elevators, taxicabs, and gas stations. Many airlines now provide live satellite TV on individual seatback television screens.

It's bad enough that American adults watch so much TV. That so many kids wallow in it veers on child abuse. Some parents speak confidently of "educational" television, an oxymoron on the order of "diet ice cream" and "congressional wisdom." Children don't become educated from watching TV, and the more TV they watch, the less educated they usually end up.

Countless studies have documented the inverse link between devotion to the boob tube and achievement in school. Researchers at Columbia University's College of Physicians and Surgeons concluded in 2007, for example, that 14-year-olds who watched one or more hours of television daily "were at elevated risk for poor homework completion, negative attitudes toward school, poor grades, and long-term academic failure." Those who watched three or more hours a day were at even greater risk for "subsequent attention and learning difficulties," and were the least likely to go to college.

In 2005, a study published in the American Archives of Pediatrics and Adolescent Medicine found that the harm caused by TV watching shows up even after correcting the data to account for students' intelligence, family conditions, and prior behavioral problems. The bottom line: "Increased time spentwatching television during childhood and adolescence was associatedwith a lower level of educational attainment by early adulthood."

The baleful effects of TV aren't limited to education. The University of Michigan Health System notes at its extensive website that kids who watch TV are more likely to smoke, to be overweight, to suffer from sleep difficulties, to have high cholesterol. If television came in a bottle, it would be illegal to sell it to children. Yet on any given day, 81 percent of 8- to 18-year-olds watch TV, and they watch it, on average, for more than three hours. Even the very youngest Americans are steeped in TV. According to their parents, 43 percent of children younger than 2 -- babies and toddlers! -- watch television every day. More than 1 in 4 have a TV set in their bedroom.

Tell the truth: Would more TV-watching have made your life better? It won't improve your kids' lives either. So why don't you do them a favor? Turn the idiot box off.

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